1. Field of the Invention
The present invention relates to the prevention of synthetic color fading in beverages. It is directed to a food coloring composition comprising a botanically derived color stabilizer and a synthetic color, as well as to a stable synthetic colored beverage containing the same and to a method of preventing color fading by including in said beverage the same.
2. Related Background Art
Color stability is an important issue in the beverage world. Both natural and synthetic (or artificial) colors are known to fade, most typically upon exposure to UV light. When beverages are packaged in glass or polyethylene terephthalate (PET) containers, they are even more susceptible to problematic color fading. The problems associated with color fading are primarily aesthetic in nature. A once vibrant color may become dull or disappear entirely; in certain circumstances, the color may be detrimentally altered, many times taking on a brownish hue. This limits the development of a wide platform of colored beverages and decreases consumer acceptability of a colored beverage.
It is believed that oxidation and/or reduction is primarily responsible for color instability or color fading. Oxidation and/or reduction can be chemically-, light- or biologically (microbial, enzyme)-induced in a given beverage, though light is the predominant initiator. Secondary chemical initiators may be present in certain beverages; these include, without limitation, ascorbic acid, hydroxymethylfurfural (HMF) and metals; these initiators work with light to fade colors.
Colors can react with HMF and other carbohydrate degradation products to form browning compounds. The mechanism of the reaction, which is very noticeable in fruit juices, is known, and it is very temperature dependent and is hastened by the presence of oxygen.
Natural colors are typically believed to fade by an oxidative mechanism. A number of solutions for color fading with respect to natural colors have been proposed.
J. G. Sweeny, et al., have identified a molecular complex, shown below, between a natural color and a flavone which is said to account for natural color protection. J. Agric. Food Chem., vol. 29, pp. 563-567 (1981).

The rearward structure is the color stabilizer quercetin-5′-sulfonic acid and the forward structure is the natural color apigeninidin. The π-π ring interaction, intermolecular hydrogen bonding, and ionic interactions are all structurally dependent.
In addition, Lenoble et al. (U.S. Pat. No. 5,908,650) have proposed the combination of an anthocyanin (a natural color) and a pigment-improving agent selected from flavonoid glycuronides and glucuronides (including 8-position compounds), galacturonides and caffeic acid derivatives in order to deepen and improve the intensity of the anthocyanin and to increase its stability. Lenoble et al. rely on a “copigmentation” of natural botanical substances with natural colors to afford protection.
Further, JP 6-93199 discloses the use of chlorogenic acid, caffeic acid or ferulic acid as an anti-fading agent for natural gardenian yellow color. Todd (U.S. Pat. No. 5,314,686) discloses that rosemary, sage and thyme have color sparing properties with respect to natural colors such as annatto, bixin, paprika and carotenoids.
What is more, Chang (U.S. Pat. No. 5,336,510) discloses the use of riboflavin (vitamin B2) as a color stabilizer in azo-colored beverages fortified with vitamin C. Onishi et al. (U.S. Pat. No. 6,379,729) disclose the use of a combination of sulfurous acid and sorbic acid to obtain a color stabilizing effect in foods or beverages colored with an anthocyanin, a coal tar color or carthamus yellow.
Color fading has been more thoroughly investigated with respect to natural colors (see above), as it is believed that synthetic colors are inherently more stable. However, color fading is problematic for synthetically colored beverages (see Onishi et al. above). Vendors of synthetic colors teach that such colors may fade by a reductive chemical mechanism.
Azo dyes, such as FD&C Red No. 40, comprise the largest group of certified synthetic colors. It is well-documented that azo compounds in the presence of oxidizing agents are easily converted to colorless substances. Further, azo compounds can be easily reduced in the presence of reducing agents as shown below:

The kinetics of the reduction is dependent on the concentration of the substrate, the nature of the reducing agent and temperature.
Triphenylmethane dyes (TPM) are characterized by three aromatic rings attached to a central carbon. In organic chemistry terms, TPM dyes may also be considered “homo-iminium” and thereby possess similar electronic density behaviors to azo dyes. That is, when the electron density is distributed throughout the entire chemical structure, visible light is absorbed in the pi orbitals to create color. This is called conjugation. If electrons are added to reduce that conjugation, color is lost.
Adding credence to the theory that color fading in synthetically colored beverages occurs primarily due to a reductive mechanism, it has been found that color fading occurs more prominently in synthetic colored beverages in the absence of oxygen, i.e., <3 ppm oxygen. Such a low oxygen content is typical of most carbonated and hot-filled beverages. Hence, anti-oxidants would not be expected to stabilize synthetic colors in a low oxygen environment.
Thus, there is a need to develop a color stabilizing agent which would lessen or prevent color fading in synthetically colored beverages.